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W212 Sudden idle Drops and surges after starting engine
Hello Guys, this is my first post on this forum, and i look forward to your help. i am asking about my dad w212. E250 CGI as i own a w124 and i do not have any experience in M271 Engine , we have recently replaced the Oil Filter Housing/Cover Seal on the car due to an oil leak and the leak is solved. however after driving the car it started random misfires which were diagnosed as a Crank shaft position sensor which obviously was contaminated with leaked oil. this was replaced by a good used one. the car ran perfect for one week and now it is performing strange on engine startup especially when cold.
the engine starts normally and idle raise as it should on cold but suddenly after 1 or 2 seconds there is some fast and random idle drops then the engine recovers. it runs nicely when driving without any problem. the problem only appears when you first start the car. The check engine light keeps coming on after this behavior. (i m waiting for the weekend so i can hook it up to my friend scanner and see which code it is throwing). please check this YouTube video that describes my problem:
So guys we hooked the car to a scanner and this is what we obtained. correct me if i am wrong but i guess it is the crankshaft position sensor itself which has defects(previously replaced with a used one) ?
The pcm is trying to adjust engine run parameters to compensate for the reading from the CPS. That was the fluctuating idle, if you looked at real time run data you'd see a lot of high and low ranges. The CPS data continued to be out of range, thus the code.
It's possible the used sensor is bad, but I suggest verifying the circuit itself is ok. Start with the connector, ensuring its clean and the wiring is intact. Continuity can be checked from the connector pins back to the pcm plug pins.
If it all worked until before you worked on the car, then it could be the sensor or connector is still damaged from oil or an inadvertently pulled wire. If you get a new sensor, I suggest an oem sensor, but then I'm one of those guys that never seems to have good luck with after market sensors. But for sure take a close look at the connector.
The car is sitting at the mechanic now and they replaced the CKPS with a new OEM but the problem is still existing. the mechanic is willing to try to replace the Cam shaft position sensors. does it make any sense?
Yes the pcm compares cam and crank rotations and looks for discrepancies.
Your mechanic should have access to vehicle wiring and connector diagrams - are they doing additional diagnosis or just installing parts? Typically almost any scan tool can capture freeze frame data that is stored when a code is thrown, this data can help focus on what was happening when the pcm determined something was out of range. Scantool that I hope a shop would have can also read real time data that can show things like crank and cam rotation, cylinder firing, etc. that can lead to an effective diagnosis.
I mention all this because too many times shops start installing parts hoping that's the fix. Maybe they will get lucky with the cam sensors but if not, then I think you need someone that can access and interpret data.
Yes the pcm compares cam and crank rotations and looks for discrepancies.
Your mechanic should have access to vehicle wiring and connector diagrams - are they doing additional diagnosis or just installing parts? Typically almost any scan tool can capture freeze frame data that is stored when a code is thrown, this data can help focus on what was happening when the pcm determined something was out of range. Scantool that I hope a shop would have can also read real time data that can show things like crank and cam rotation, cylinder firing, etc. that can lead to an effective diagnosis.
I mention all this because too many times shops start installing parts hoping that's the fix. Maybe they will get lucky with the cam sensors but if not, then I think you need someone that can access and interpret data.
Hello. They changed the cam sensor and no luck. Unfortunately here in my country it is always done like this by throwing parts. I ll have to take it to the dealer. The mechanic is telling me now that he s suspecting the cam adjsuters and maybe a slip of the timing chain. But i doubt as the chain was replaced sometime ago as a preventive maintainance and the adjusters were in good conditions. I can t find that he s thinking logically. If the issue was that advanced and timing related it shall happen frequently and not only on cold starts. I am still suspecting a wiring issue or corrosion due to the oil leak. Do you guys think that it can be cam related? Souldn t the scanner throw a code related to the cam sensor instead of pointing to the crank readings. in this case can a flywheel go bad causing an error in the readings?
My next step will be the mb dealer i guess.
My friend, take it in and get a proper diagnosis, otherwise you'll be spending money to support a guessing mechanic. Slipped chain would cause other issues and a scantool would reveal where the timing is sitting and/or changing, plus the car would not run very well.
I understand the dealer is a high cost but sometimes paying for the right diagnosis up front is worth it.
Flexplates (flywheel) can get cracked or can possibly get a chipped or broken tooth on the ring gear. Usually a broken tooth shows up in hearing the starter slip as the starter gear hits the space where the flexplate tooth used to be. There should be an inspection cover at the bellhousing that allows visual inspection of the ring gear as the engine is turned by hand or a camera probe can be used in the hole where the CPS goes.
But all this may be getting ahead of ourselves, get it evaluated first.
My friend, take it in and get a proper diagnosis, otherwise you'll be spending money to support a guessing mechanic. Slipped chain would cause other issues and a scantool would reveal where the timing is sitting and/or changing, plus the car would not run very well.
I understand the dealer is a high cost but sometimes paying for the right diagnosis up front is worth it.
Flexplates (flywheel) can get cracked or can possibly get a chipped or broken tooth on the ring gear. Usually a broken tooth shows up in hearing the starter slip as the starter gear hits the space where the flexplate tooth used to be. There should be an inspection cover at the bellhousing that allows visual inspection of the ring gear as the engine is turned by hand or a camera probe can be used in the hole where the CPS goes.
But all this may be getting ahead of ourselves, get it evaluated first.
Hello friend. The issue is solved. I measuresld the continuity between CKPS plug and the ECM plug and i got some high resistance. Both plugs were corroded with antifreez from the leak. Just cleaned them and issue is solved. The car ran like a charm. Thank you all for your support.
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